A player piano, or automatic performance piano, has two functioning modes: in the recording mode the piano records a music being played by a person while in the playing mode, the piano either plays a prerecorded music or is driven by some external musical signals. In the recording mode, it is necessary to sense the changing position of the keys being played and to convert this information into electrical recording signals. FIG. 14 shows a conventional mechanism for providing this type of sensing action. The player piano 71 in this figure consists of a key board having a number of keys 73, a striking mechanism 77, the hammer head 75, the string 79 and a damper head 78.
Each of the keys 73 is supported at the balancing fulcrum 81, and when either the key 73 is manually pressed down or a solenoid 83 causes the plunger to push up the key 73, this key motion is transmitted to the hammer head 75 and the damper head 78 through the striking mechanism 77, resulting in the hammer head 75 striking the string 79 as the damper head 78 leaves the string 79.
Each key 73 is provided with a shutter 87, on its bottom side, to act on a light beam in combination with a transmission-type photo-interrupter 89. The output from this photo-interrupter 89 is forwarded to a controller 85 which is programmed to recognize the position of the key 73.
In the playing mode, to reproduce the performance style it is not sufficient simply to sense the static position of the key 73, whether the key is in the resting position or in the extreme down stroke position. Such performance data must be translated in terms of the duration and velocity of a key stroke. However, in the conventional player piano 71 described above, it was not possible to obtain such performance-style data, because of the inherently limited ability of the combined photo-interrupter 89 and shutter 87 mechanism, which can only detect the static position information of the key 73 and not the dynamic, time-dependent information of the key movement. A solution to this problem, for example, may be to provide each key with multiple shutters to detect progressive changes in the key position, but such a method would encounter basic difficulties of maintaining accuracy and long-term reliability of a multiple-sensor mechanism. Furthermore, such a mechanism presents production difficulties due to the fact that multiple shutters 87 must be installed on the bottom side of each key 73, making not only the installation but also the inspection procedures complex and time-consuming.